Baking furnace

ABSTRACT

A baking furnace for carbonaceous bodies, such as electrodes for the steel industry, having metal flues extending therethrough for conveying the baking heat to the baking media that surrounds the bodies. Inserts of heat conductive material are strategically placed in the media so as to facilitate the distribution of heat from the flues to the area of the bodies and to obtain a uniformity of baking temperature therearound.

inventor Appl. No.

Filed Patented Assignee ite Sites Pteint Alien C. Goodrich East Aurora,NM.

Dec. 20v 1968 May I l, 197i The Carlmrundum Company Niagara Falls, NX.

BAKING FURNACE 7 Claims, 3 Drawing Figs.

US. Cl Int. Cl Field of Search...

\unnuu unump [56] References Cited UNITED STATES PATENTS 3.048.382 8/ l962 Mansfield 2o3/4l 3, l 42,482 7/ l 964 Kcnan 263/41 3,448,97l 6/ l969 Renkey 263/41 Primary Examiner-John J. Camby AttorneyK. W. BrownellABSTRACT: A baking furnace for carbonaceous bodies, such as electrodesfor the steel industry, havingmetal flues extending therethrough forconveying the baking heat to the baking media that surrounds the bodies.Inserts of heat conductive material are strategically placed in themedia so as to facilitate the distribution of heat from the flues to thearea of the bodies and to obtain a uniformity of baking temperaturetherearound.

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2 Sheets-Sheet 1 M'I'IIII'IIIIII'II) I NVEN TOR zm c. 6000 9704 ATTORNEYPatented May 11,-1971 Patented May 11, 1971 2 Sheets-Sheet 2 INVEN'H)?fLl-fN c. 6000/ /06 ATTORNEY BAKING FURNACE BACKGROUND OF THE INVENTIONThis invention relates to an improvement in baking furnaces particularlyconstructed for the processing of carbonaceous bodies such as electrodesfor the steel industry. The practice of constructing baking furnaces toprocess carbonaceous bodies, essentially has been to construct severalnonmetallic refractory brick compartments or chambers into which thegreen" carbonaceous bodies are placed. The green" bodies are usuallypacked in a mixture of sand and coke to prevent oxidation, to supportthe bodies, and to prevent slump when the furnace temperature risesabove the melting point of the binders. Heated gases are typicallycirculated around these chambers along the sidewalls of the furnace. Insome cases, gases pass under the chamber and also through thepartitioning flue walls which divide the furnace into individualchambers. The green carbonaceous bodies are baked by the heat from thecirculating gases. These furnaces were originally constructed in asomewhat permanent manner which involved considerable nonmetallic brickand flue installation requiring great time and expense.

Furnaces of such a permanent nature were seldom efficient for bakinggreen stock of widely differing sizes. Nonuniformity in the speed andextent of baking was a frequent result. High scrap losses and nonuniformphysical properties resulted.

The size of bodies being baked in such a furnace is also limited by thegeometry of the chambers. Special furnaces were required to bakeodd-size pieces. Nonmetallic refractory brick flues are expensive toconstruct and maintain.

Metallic flues were installed in later furnaces to overcome some of thedifficulties enumerated above. These metal flues were less expensive,more easily installed, more flexible, and more thermally efficient.Baking furnaces with metal flue ducts do not, however, result in moreuniform heating of the bodies being baked; On the contrary, the improvedthermal conductivity resulted in hot spots close to the flues. For somepacking geometrics, the carbon bodies may be heated more rapidly atpositions closer to the flue ducts. The installation of more highlyconductive packing materials tends to aggravate this localized heating.The metallic flues overcome many costly construction, maintenance, andchanging packing geometry problems, but at the same time, theyintroduced local hot spots.

SUMMARY OF THE INVENTION One object of this invention is to improve theconstruction of baking furnaces for the purposes described and to obtaina more uniform distribution of heat to the bodies placed therein forbaking.

Another object of the invention is to obtain a more uniform heating ofthe green carbonaceous bodies than has been possible heretofore withprior baking furnaces for the purpose.

These objects may be accomplished by providing directional thermalconductivity through inserts installed in the fumace in a manner whichwill remove the heat from the conductive or metallic flues anddistribute the heat to special points in the baking media so that thebaking carbonaceous bodies will be at a more nearly uniform temperaturelevel.

The invention relates to an improved furnace which is particularlyadapted to bake carbonaceous bodies of widely differing shapes andsizes, and to accomplish this under conditions of increased thermalefficiency, temperature uniformity, increased furnace capacity. andreduced furnace construction and operational costs. The inventionrelates further to the use of the described furnace while achievingimproved quality in the baked bodiesproduced. Particularly, theinvention relates to directional thermal conductivity implemented by afurnace which includes specific inserts which may be more conductivethan the packing media as appendages on or adjacent to the flue ducts todirect the flow of heat to special points in the charge in a mannerwhich reduces the temperature differences thermal conductivityimplemented by a furnace modification which includes nonconductiveinserts that are less conductive than the packing media, positioned inthe packing media between the flue ducts and the carbonaceous bodiesbeing baked in a manner which reduces the temperature differences in thebaking stock.

BRIEF DESCRIPTION OF DRAWINGS One embodiment of the invention isillustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view, partly in section, of a baking furnace towhich the invention may be applied;

FIG. 2 is a similar view, illustrating the application of the conductiveinserts to the furnace; and

FIG. 3 is a diagrammatic plan view, showing the directional heatconductors in relation to the flues and bodies.

DETAILED DESCRIPTION OF DISCLOSURE Referring to the embodiment of theinvention illustrated in FIGS. 1 and 2, the furnace may be madetypically by pouring concrete for the outer frame or shell 1 of thedimensions desired. This shell 1 may be provided with a lining 2 alongthe sides and bottom of the shell as by a system of nonmetallicrefractory bricks. The bottom of this refractory lining forms a systemof channels or tunnels 3 which are in open communication with conductiveor metallic flues 4 extending vertically within the chamber formed inthe outer shell 1.

This chamber is adapted to receive the green" bodies which may be madeof carbonaceous material when these are adapted to fomr electrodes forthe steel industry, as an example. Ordinarily, these bodies are packedin a mixture of sand and coke which fills the chamber around the bodiesand between and around the flues 4, but which is omitted from theillustrations in FIGS. 1 and 2 for cleamess. The flues 4 extend to thetop of the charge of sand and coke and of the carbonaceous bodies andare open inside the chamber of the furnace. The top of the furnace isshown as bridged over by a refractory-lined hogback cover 5.

The furnace is heated by a firebox or combustion zone 6 from which, bymeans of a fan or other suitable draft means, the heated gases areforced through an opening 7 under the hogback cover 5, down the flues 4,through the tunnels 3, thence to a suitable stack (not shown), or thegas may be recycled to the combustion zone. The direction of hot gasflow may be reversed if desired. Flues or other gas channels are placedfrequently in the outer furnace shell.

As illustrated in FIG. 2, conductive inserts or slabs, indicated at 8,are mounted in upright relation between the adjacent flues 4 and in apattern substantially to surround the slabs may be any of a wide varietyof sizes and shapes depending on the particular packing geometry. Theconductive inserts may also be constructed of metals such as steel,stainless I steel, and other relatively conductive materials. Theseinserts may be attached to the flue pipe. or placed in special ways toaccomplish the directional conductivity within the packing medium.

After the conductive or metal flues are positioned in a manner whichprovides the most efficient use of the space with respect to the sizeand shape of the green carbon bodies to be baked, the packing materialsand the bodies to be baked in the baking stock. The invention alsorelates to directional are placed in the furnace in accordance withconventional techniques employed in the art. The number of fluesemployed and their positioning, and the positioning of the carbon bodieswill, of course, be selected with regard to the baking cycle to befollowed, to promote evenness of baking of the carbon bodies. Theconductive inserts will be installed, based on an empirical andmathematical study of the overall thermal conductivity and temperatureprofile of the systems during the baking period and in such a mannerthat the temperatures of the surfacesof the green carbon bodies will benearly equal or such that their rate of temperature rise will becommensurate with the desired baking cycle and the production ofdesirable physical properties in the baked product.

The inserts 8 may be fabricated of a suitable thermally conductive metalthat is more heat-conductive than the packing media, such as sand andcoke. However, it is also possible, according to this invention, to useconductive nonmetals, such as graphite.

Under some conditions, it may be found desirable to use other relativevariations'f o'f heat conductivity, according to the desired temperaturegradients within the furnace. For example, the inserts may be lessconductive than the packing media, or fabricated from thermallyresistant materials such as certain ceramic materials including rockwooland mica. lnserts may be used which are chemically changed in thepresence of heat and in such manner that heat is absorbed by the insertand thereby alters the thermal gradient profile within the packingmedia, thereby adjusting the rate of flow of heat to the carbonaceousbodies that constitute the furnace charge. I

Inserts maybe used which contain passageways for cooling media,including liquids and gases, which may be but are not necessarily.volatile, such as water, and may include inert gases, hydrocarbons, airand products of combustion.

The objective of this invention is the uniform and efficient transfer ofheat from the hot gases originating in the combustion zone to the bakingcarbonaceous bodies. It is apparent that the inserts may be extendedinto the hot gas zones, such as into the hogback, and from here beextended into the packing area, thus improving the efficiency of theheat transfer,

The tops of the metal flues should typically be about flush with the topof the packing media cover placed in the furnace. This cover is normallya layer of sand on top of the packing media. The packing media may be amixture in varying proportions of sand and coke. This packing mediasurrounds the stock being baked. Its function is to serve as a heattransfer media to minimize or prevent the oxidation of the stock beingbaked and to support the green bodies while they are being baked. it andthe sand cover should, of course, be kept out of the flue system. Thepacking media is thermally treated to reduce shrinkage during the bakingcycle. It is carefully settled and compacted about the green bodies in amanner that will prevent slumping of the green body. According to thisinvention, more uniform temperatures and more efficient bake furnaceutilization can be achieved by employing conductive inserts of metal,graphite, or other thermally conductive materialstrategically'placed inthe charge so as to reduce the temperature difference at points in thepacking media.

During the baking of large electrodes of or more inches in diameter, itis necessary to reduce the temperature rise to approximately 1 per hourin conventional furnaces to prevent excessive scrap losses. The rate oftemperature rise is a function of the size of the stock being baked andthe packingpattern. The baking process involves chemical and physicalchanges which involve the liberation of gases and changes in thedimensions of the body. Unless the gases are evolved at a slow uniformrate, so that the dimensional changes are quite uniform throughout thecharge, damage to the physical properties and cracking of the stock willusually result. An increase in scrap level and poor quality product canmake the process less economical.

The thermal conductivity of the carbonaceous charge (3.0

B.t.u,/hr./sq.ft./F./ft. can be far greater than that of the packingmedium which IS normally a mixture of sand (0.19

B.t.u./hr./sq.ft./F./ft.) and coke (0.55 B.t.u./hr./sq.ft./F./ft.)particles. Poor thermal conductivity of the packing medium can result inundesirable temperature differences in the charge stock if the fluetemperatures are raised too rapidly. It does not normally help to reducethe resistance of the packing medium because this increases thepossibility of hot spots in the baking body close to the flue ducts.

The installation of these directional heat conductors reduces thetemperature differences in the packing medium. The flue temperatures canbe raised more rapidly without damaging the green bodies. The furnaceefficiency can, therefore, be increased by decreasing furnace residencetime and by reducing scrap losses.

FIG. 3 shows diagrammatically the temperature effects obtained withdirectional heat conductors in the furnace according to this invention.lso-temperature lines reveal the change in surface temperatureuniformity resulting from the use of directional heat conductors. Thedifference between iso-temperature lines decreases as temperaturegradients increase.

Thus, according to this invention, a more uniform heating of the greencarbonaceous bodies can be obtained by employing a system of conductiveinserts in the furnace packing media. These inserts provide directionalthermal conductivity. The inserts are installed in a manner which willremove the heat from the conductive or metallic flues and distribute theheat to special points in the packing media so that it will reach thebaking carbonaceous bodies at a more nearly uniform temperature level.

While the invention has been illustrated and described in oneembodiment, it is recognized that variations and changes may be madetherein without departing from the invention as set forth in the claims.

lclaim:

l. A baking furnace for carbonaceous bodies, comprising a chamberadapted to, receive packing media for at least partially surrounding acarbonaceous body, heating means for the body including spaced fluesextending in position in the chamber to be surrounded by the packingmedia, and heat conducting bodies extending in bridging relation betweenadjacent flues for distributing heat from the flues through the packingmedia to the carbonaceous body, said heat conducting bodies extendingalso substantially parallel with said flues.

2. A baking furnace for carbonaceous bodies according to claim 1,wherein the packing media comprises discrete material and the flues aremetal and extend through the discrete material.

3. A baking furnace for baking carbonaceous bodies, comprising a chamberfor receiving the bodies, heating means including flue ducts in thechamber and exhaust means, packing media for surrounding the bodies, andheat-conducting inserts in the packing media between adjacent flue ductsin position for directing the flow of heat from the flue ducts to pointswithin the packing media and thereby to direct the flow of heat throughsaid inserts and media to the carbonaceous bodies, whereby thetemperature gradients within the furnace and bodies are reduced, saidinserts extending substantially parallel with said flue ducts.

4. A baking furnace according to claim 3, wherein the inserts have adifferent rate of heat conduction than the packing media.

5. A baking furnace according to claim 3, wherein the inserts comprisethermally conductive materials more conductive to heat than the packingmedia.

6. A baking furnace according to claim 3, wherein the inserts areattached to the flue ducts and extend laterally therefrom in the form offins to direct the flow of heat to special points in the media.

7. A baking furnace according to claim 3, wherein the inserts extendalong the flue ducts to the region of the chamber outside of the packingmedia.

2. A baking furnace for carbonaceous bodies according to claim 1,wherein the packing media comprises discrete material and the flues aremetal and extend through the discrete material.
 3. A baking furnace forbaking carbonaceous bodies, comprising a chamber for receiving thebodies, heating means including flue ducts in the chamber and exhaustmeans, packing media for surrounding the bodies, and heat-conductinginserts in the packing media between adjacent flUe ducts in position fordirecting the flow of heat from the flue ducts to points within thepacking media and thereby to direct the flow of heat through saidinserts and media to the carbonaceous bodies, whereby the temperaturegradients within the furnace and bodies are reduced, said insertsextending substantially parallel with said flue ducts.
 4. A bakingfurnace according to claim 3, wherein the inserts have a different rateof heat conduction than the packing media.
 5. A baking furnace accordingto claim 3, wherein the inserts comprise thermally conductive materialsmore conductive to heat than the packing media.
 6. A baking furnaceaccording to claim 3, wherein the inserts are attached to the flue ductsand extend laterally therefrom in the form of fins to direct the flow ofheat to special points in the media.
 7. A baking furnace according toclaim 3, wherein the inserts extend along the flue ducts to the regionof the chamber outside of the packing media.